The overall goal of this research project is to provide an understanding of the molecular details and control features of the reactions of vitamin A known as the visual cycle. The major emphasis of the work is associated with the hypothesis that vitamin A transport and metabolism is facilitated by a group of retinoid-binding proteins which are postulated to solubilize and carry the vitamin during inter- and intracellular transport and to be involved in the control of its enzymatic transformation. Each of the specific aims pursues an aspect of this central theme. Independent confirmation of a role for Muller cells in the metabolism of vitamin A will be sought employing Muller cells in culture or isolated from suspension of disaggregated retinal cells. Antibodies specific for four different retinoid-binding proteins (CRBP, cellular retinol-binding protein; CRABP, cellular retinoic acid-binding protein; CRALBP, cellular retinaldehyde-binding protein; IRBP, interphotoreceptor retinoid-binding protein) will be used to assess whether a variation in their level occurs following a physiologic (bleaching), nutritional (vitamin A deficiency) or pathologic challenge. The endogenous retinoids associated with three of the retinoid-binding proteins (CRBP, CRALBP and IRBP) will be examined from dark-adapted and bleached cattle eyes or eyes from laboratory animals. A study of the role of retinoid-binding proteins as substrate carriers for enzymatic reactions will be continued with emphasis placed on attempts to demonstrate the specificity of interaction between binding protein and enzyme and the linking of two or more enzymatic reactions. Amino acid sequence studies will be carried out on CRALBP to determine if it is a member of the family of structurally related proteins which now includes CRABP, CRBP, Z-protein and myelin P2 protein. 125I-SRBP (serum retinol-binding protein) will be labeled with a photosensitive ligand and used to probe the molecular nature of the SRBP receptor reported to be present on the basal surface of retinal pigment epithelium.